1. Field of the Invention
The invention relates to an electrode consisting of at least three elements, and in particular to a neutral electrode for a High Frequency (HF) surgical instrument in which the electrode elements are arranged on a common flexible carrier.
2. Description of the Prior Art
A neutral electrode of the above mentioned kind which includes three planar electrode elements is known, for example, from U.S. patent application Ser. No. 929,561 filed Nov. 10, 1986 (corresponding with the present Assignee's German Patent Publication DE-OS No. 35 44 443), now U.S. Pat. No. 4,754,757.
In connection with HF surgical instruments it has been found that a multiple element design for the neutral electrode is desirable if the intent is to ascertain with a monitor circuit whether, during the HF surgical procedure, the neutral electrode is in contact with the patient over a large area and not only in some points. Such a monitor circuit for a three-element neutral electrode is shown in FIG. 4 of the above-mentioned DE-OS No. 35 44 443 and described in greater detail in the related text.
If a multi-element planar electrode having rectangular electrode elements is used and if this planar electrode is applied on the thigh of a patient, two application directions, in principle, are possible. In one application direction the three electrode elements are aligned in the direction of the longitudinal axis of the thigh. This case should be called one of improper application, for the high frequency going out from the surgical field, for example in the abdominal area, will reach the three electrode elements with different intensities. With respect to monitoring the proper contact of the neutral electrode with the patient, this can lead to erroneous measurements. In the other case, the three electrode elements are applied transversely to the longitudinal direction of the thigh. This case can be referred to as one of proper application, because in this case, the three electrode elements are reached by the high frequency going out from the surgical field approximately with the same intensity, given identical surface areas.
In hospitals, the application of the neutral electrode is frequently carried out by auxiliary personnel. In order to avoid the possibility of committing an error and, hence, loss of time in preparing a patient for the surgical procedure, a possible solution should be sought as to how the individual electrode elements, independently of the orientation of the neutral electrode with respect to the longitudinal axis of, for example, the thigh, can be impressed with the same HF intensity (power). As a first approximation it should be assumed that all of the electrode elements have the same surface area.
An object of the invention, therefore, is to develop an electrode of at least three elements so that a substantially uniform distribution of the high frequency energy going out from the surgical field onto the electrode elements is achieved. In this connection it is basically irrelevant in which orientation with respect to its normal the neutral electrode is applied on the patient.